1. Field of the Invention
This invention relates to automatic fuel ignition systems, and more particularly, to a fail-safe, proven pilot ignition system providing automatic shutoff of fuel supply to pilot and main burner sources in the event of loss of pilot flame or ignition sparks.
2. Description Of The Prior Art
Many manual and automatic fuel ignition systems have been proposed in the prior art. In manual ignition systems, for example, ignition of a pilot fuel is accomplished by manually operating a valve of the pilot source to permit fuel from a pilot source to be ignited. Once a pilot flame is established, the continued presence of the pilot flame is sensed by a thermocouple to enable the pilot valve to remain operated.
At the present time, many existing manually operated pilot sources are being converted to provide automatic operation. Such conversion generally requires the addition of two pair of electrodes to the system, one pair of electrodes for igniting the fuel and another pair of electrodes for sensing the presence of the pilot flame. Such electrodes must be positioned adjacent the outlet of the pilot source in the space provided for the thermocouple. However, in existing pilot burner apparatus, it is generally not possible to physically locate two pair of electrodes in the space provided for the thermocouple. Therefore, it would be desirable to provide an automatic fuel ignition system which requires only a single pair of electrodes to provide both fuel ignition and flame sensing functions so that such electodes may be located in the space provided for the thermocouple in existing pilot burner apparatus.
Although automatic fuel ignition systems are more desirable than manual systems from the convenience standpoint, automatic systems require means for automatically controlling the shutoff of the supply of fuel to the pilot and main burners in the event of flame out. For example, many automatic systems employ a warp switch which is operable in the event of a flame out to effect shutoff of the supply of fuel to the pilot burner whenever ignition sparks provided by the spark generating circuit fail to establish a pilot flame within a predetermined time. However, if the warp switch is inoperative due to an open circuit condition of the warp switch heater circuit, for example, failure of the warp switch to operate will enable the fuel to be supplied to the pilot burner until the ignition spark circuit is enabled to generate ignition sparks and until reignition of the pilot flame occurs.
In addition, if the ignition spark generating circuit malfunctions such that ignition sparks are not provided when required, fuel emanating from the pilot source is wasted. Accordingly, it would be desirable to have an automatic fuel ignition system which automatically checks the operability of the warp switch and the ignition spark generating circuit. It would also be desirable to have an automatic fuel ignition system which effects total shut down of the fuel supply to the system in the event of loss of pilot flame or loss of ignition sparks.